Helicobacter pylori-induced tyrosine phosphorylation of IKKβ contributes to NF-κB activation

Dual-specific autophosphorylation of kinase IKK2 enables phosphorylation of substrate IκBα through a phosphoenzyme intermediate

Rapid and high-fidelity phosphorylation of two serines (S32 and S36) of IκBα by a prototype Ser/Thr kinase IKK2 is critical for fruitful canonical NF-κB activation. Here, we report that IKK2 is a dual specificity Ser/Thr kinase that autophosphorylates itself at tyrosine residues in addition to its activation loop serines. Mutation of one such tyrosine, Y169, located in proximity to the active site, to phenylalanine, renders IKK2 inactive for phosphorylation of S32 of IκBα. Surprisingly, auto-phosphorylated IKK2 relayed phosphate group(s) to IκBα without ATP when ADP is present. We also observed that mutation of K44, an ATP-binding lysine conserved in all protein kinases, to methionine renders IKK2 inactive towards specific phosphorylation of S32 or S36 of IκBα, but not non-specific substrates. These observations highlight an unusual evolution of IKK2, in which autophosphorylation of tyrosine(s) in the activation loop and the invariant ATP-binding K44 residue define its signal-responsive substrate specificity ensuring the fidelity of NF-κB activation.

Gastric Epithelial Barrier Disruption, Inflammation and Oncogenic Signal Transduction by Helicobacter pylori

Helicobacter pylori exemplifies one of the most favourable bacterial pathogens worldwide. The bacterium colonizes the gastric mucosa in about half of the human population and constitutes a major risk factor for triggering gastric diseases such as stomach cancer. H. pylori infection represents a prime example of chronic inflammation and cancer-inducing bacterial pathogens. The microbe utilizes a remarkable set of virulence factors and strategies to control cellular checkpoints of inflammation and oncogenic signal transduction. This chapter emphasizes on the pathogenicity determinants of H. pylori such as the cytotoxin-associated genes pathogenicity island (cagPAI)-encoded type-IV secretion system (T4SS), effector protein CagA, lipopolysaccharide (LPS) metabolite ADP-glycero-β-D-manno-heptose (ADP-heptose), cytotoxin VacA, serine protease HtrA, and urease, and how they manipulate various key host cell signaling networks in the gastric epithelium. In particular, we highlight the H. pylori-induced disruption of cell-to-cell junctions, pro-inflammatory activities, as well as proliferative, pro-apoptotic and anti-apoptotic responses. Here we review these hijacked signal transduction events and their impact on gastric disease development.

Mechanism of action of NF-κB related cell signaling pathways in progression of gastritis to carcinoma

Gastric cancer (GC) is a major global public health problem. The evolvement pattern of "superficial gastritis-chronic atrophic gastritis-intestinal metaplasia-dysplasia-gastric carcinoma" is common in related gastric diseases. As a key factor involved in systemic stress response, inflammatory response, and apoptosis, the regulation of NF-κB related to inflammation and apoptosis is a necessary link between inflammation and cancer progression. NF-κB is activated in most solid tumors and lymphomas. In the critical mechanism of gastric cancer induced by gastritis with various etiologies, the upstream and downstream molecules in the NF-κB signaling pathway are changed, and the cells are exposed to the microenvironment of inflammatory response for a long time, which ultimately leads to the development of their carcinogenic potential. This article discusses the mechanism of NF-κB in the key risk factors for the progression of gastric disease.

Importance of cortactin for efficient epithelial NF-ĸB activation by Helicobacter pylori, Salmonella enterica and Pseudomonas aeruginosa, but not Campylobacter spp

Transcription factors of the nuclear factor kappa‐light‐chain‐enhancer of activated B cells (NF-ĸB) family control important signaling pathways in the regulation of the host innate immune system. Various bacterial pathogens in the human gastrointestinal tract induce NF-ĸB activity and provoke pro-inflammatory signaling events in infected epithelial cells. NF-ĸB activation requires the phosphorylation-dependent proteolysis of inhibitor of ĸB (IĸB) molecules including the NF-ĸB precursors through ubiquitin-mediated proteolysis. The canonical NF-ĸB pathway merges on IĸB kinases (IKKs), which are required for signal transduction. Using CRISPR-Cas9 technology, secreted embryonic alkaline phosphatase (SEAP) reporter assays and cytokine enzyme-linked immunosorbent assay (ELISA), we demonstrate that the actin-binding protein cortactin is involved in NF-ĸB activation and subsequent interleukin-8 (IL-8) production upon infection by Helicobacter pylori, Salmonella enterica and Pseudomonas aeruginosa. Our data indicate that cortactin is needed to efficiently activate the c-Sarcoma (Src) kinase, which can positively stimulate NF-ĸB during infection. In contrast, cortactin is not involved in activation of NF-ĸB and IL-8 expression upon infection with Campylobacter species C. jejuni, C. coli or C. consisus, suggesting that Campylobacter species pluralis (spp.) induce a different signaling pathway upstream of cortactin to trigger the innate immune response.

Gastric Cancer in the Era of Immune Checkpoint Blockade

Gastric cancer (GC) is one of the most important malignancies worldwide because of its high incidence and mortality. The very low survival rates are mainly related to late diagnosis and limited treatment options. GC is the final clinical outcome of a stepwise process that starts with a chronic and sustained inflammatory reaction mounted in response to Helicobacter pylori infection. The bacterium modulates innate and adaptive immunity presumably as part of the strategies to survive, which favors the creation of an immunosuppressive microenvironment that ultimately facilitates GC progression. T-cell exhaustion, which is characterized by elevated expression of immune checkpoint (IC) proteins, is one of the most salient manifestations of immunosuppressive microenvironments. It has been consistently demonstrated that the tumor-immune microenvironment(TIME)‐exhausted phenotype can be reverted by blocking ICs with monoclonal antibodies. Although these therapies are associated with long-lasting response rates, only a subset of patients derive clinical benefit, which varies according to tumor site. The search for biomarkers to predict the response to IC inhibition is a matter of intense investigation as this may contribute to maximize disease control, reduce side effects, and minimize cost. The approval of pembrolizumab for its use in GC has rocketed immuno-oncology research in this cancer type. In this review, we summarize the current knowledge centered around the immune contexture and recent findings in connection with IC inhibition in GC.

Priming the seed: Helicobacter pylori alters epithelial cell invasiveness in early gastric carcinogenesis

Helicobacter pylori (H. pylori) infection is a well-established risk factor for the development of gastric cancer (GC), one of the most common and deadliest neoplasms worldwide. H. pylori infection induces chronic inflammation in the gastric mucosa that, in the absence of treatment, may progress through a series of steps to GC. GC is only one of several clinical outcomes associated with this bacterial infection, which may be at least partially attributed to the high genetic variability of H. pylori. The biological mechanisms underlying how and under what circumstances H. pylori alters normal physiological processes remain enigmatic. A key aspect of carcinogenesis is the acquisition of traits that equip preneoplastic cells with the ability to invade. Accumulating evidence implicates H. pylori in the manipulation of cellular and molecular programs that are crucial for conferring cells with invasive capabilities. We present here an overview of the main findings about the involvement of H. pylori in the acquisition of cell invasive behavior, specifically focusing on the epithelial-to-mesenchymal transition, changes in cell polarity, and deregulation of molecules that control extracellular matrix remodeling.

Role of LPS-elicited signaling in triggering gastric mucosal inflammatory responses to H. pylori: modulatory effect of ghrelin

Infection with Helicobacter pylori is a primary culprit in the etiology of gastric disease, and its cell-wall lipopolysaccharide (LPS) is recognized as a potent endotoxin responsible for triggering a pattern of the mucosal inflammatory responses. The engagement by the LPS of gastric mucosal Toll-like receptor 4 (TLR4) leads to initiation of signal transduction events characterized by the activation of mitogen-activated protein kinase (MAPK) cascade, induction of phosphoinositide-specific phospholipase C (PLC)/protein kinase C (PKC)/phosphatidylinositol 3-kinase (PI3K) pathway, and up-regulation in Src/Akt. These signaling events in turn exert their influence over H. pylori-elicited excessive generation of NO and PGE2 caused by the disturbances in nitric oxide synthase and cyclooxygenase isozyme systems, increase in epidermal growth factor receptor transactivation, and the induction in matrix metalloproteinase-9 (MMP-9) release. Interestingly, the extent of gastric mucosal inflammatory response to H. pylori is influenced by a peptide hormone, ghrelin, the action of which relays on the growth hormone secretagogue receptor type 1a (GHS-R1a)-mediated mobilization of G-protein dependent transduction pathways. Yet, the signals triggered by TLR-4 activation as well as those arising through GHS-R1a stimulation converge at MAPK and PLC/PKC/PI3K pathways that form a key integration node for proinflammatory signals generated by H. pylori LPS as well as for those involved in modulation of inflammation by ghrelin. Hence, therapeutic targeting these signals' convergence and integration node could provide a novel and attractive opportunities for developing more effective treatments of H. pylori-related gastric disease.

NF-κB Signaling in Gastric Cancer

Gastric cancer is a leading cause of cancer death worldwide. Diet, obesity, smoking and chronic infections, especially with Helicobacter pylori, contribute to stomach cancer development. H. pylori possesses a variety of virulence factors including encoded factors from the cytotoxin-associated gene pathogenicity island (cagPAI) or vacuolating cytotoxin A (VacA). Most of the cagPAI-encoded products form a type 4 secretion system (T4SS), a pilus-like macromolecular transporter, which translocates CagA into the cytoplasm of the host cell. Only H. pylori strains carrying the cagPAI induce the transcription factor NF-κB, but CagA and VacA are dispensable for direct NF-κB activation. NF-κB-driven gene products include cytokines/chemokines, growth factors, anti-apoptotic factors, angiogenesis regulators and metalloproteinases. Many of the genes transcribed by NF-κB promote gastric carcinogenesis. Since it has been shown that chemotherapy-caused cellular stress could elicit activation of the survival factor NF-κB, which leads to acquisition of chemoresistance, the NF-κB system is recommended for therapeutic targeting. Research is motivated for further search of predisposing conditions, diagnostic markers and efficient drugs to improve significantly the overall survival of patients. In this review, we provide an overview about mechanisms and consequences of NF-κB activation in gastric mucosa in order to understand the role of NF-κB in gastric carcinogenesis.

Helicobacter pylori: A Paradigm Pathogen for Subverting Host Cell Signal Transmission

Helicobacter pylori colonizes the gastric mucosa in the human stomach and represents a major risk factor for peptic ulcer disease and gastric cancer. Here, we summarize our current knowledge of the complex impact of H. pylori on manipulating host signalling networks, that is, by the cag pathogenicity island (cagPAI)-encoded type IV secretion system (T4SS). We show that H. pylori infections reflect a paradigm for interspecies contact-dependent molecular communication, which includes the disruption of cell-cell junctions and cytoskeletal rearrangements, as well as proinflammatory, cell cycle-related, proliferative, antiapoptotic, and DNA damage responses. The contribution of these altered signalling cascades to disease outcome is discussed.

miR-508-3p concordantly silences NFKB1 and RELA to inactivate canonical NF-κB signaling in gastric carcinogenesis

Background

NF-κB signaling pathway plays an important role in gastric carcinogenesis. The basic expression and functional role of NFKB1 and RELA (components of canonical NF-κB pathway) in gastric cancer (GC) have not been well elucidated. In this study, the role of NFKB1 and RELA in gastric tumorigenesis will be investigated and their regulation by microRNAs (miRNAs) will be deeply explored.

Methods

The mRNA and protein expression of NFKB1 and RELA were investigated by qRT-PCR and Western blot in GC cell lines and primary tumors. The functional roles of NFKB1 and RELA in GC were demonstrated by MTT proliferation assay, monolayer colony formation, cell invasion and migration, cell cycle analysis and in vivo study through siRNA mediated knockdown. Identification of NFKB1 as a direct target of tumor suppressor miRNA miR-508-3p was achieved by expression regulation assays together with dual luciferase activity experiments.

Results

NFKB1 and RELA were up-regulated in GC cell lines and primary tumors compared with normal gastric epithelium cells and their upregulation correlation with poor survival in GC. siRNA mediated knockdown of NFKB1 or RELA exhibited anti-oncogenic effect both in vitro and in vivo. NFKB1 was further revealed to be a direct target of miR-508-3p in gastric tumorigenesis and their expression showed negative correlation in primary GC samples. miR-508-3p was down-regulated in GC cells compared with normal gastric epithelium samples and its ectopic expression in GC cell lines also exerts tumor suppressor function. NFKB1 re-expression was found to partly abolish the tumor-suppressive effect of miR-508-3p in GC.

Conclusion

All these findings supports that canonical NF-κB signaling pathway is activated in GC at least by the inactivation of miR-508-3p and this might have therapeutic potential in GC treatment.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-016-0493-7) contains supplementary material, which is available to authorized users.

TLR9 and NF-κB are partially involved in activation of human neutrophils by Helicobacter pylori and its purified DNA

Helicobacter pylori infection represents one of the most common bacterial infections worldwide. The inflammatory response to this bacterium involves a large influx of neutrophils to the lamina propria of the gastric mucosa. However, little is known about the receptors and molecular mechanisms involved in activation of these neutrophils. In this study, we aimed to determine the role of toll-like receptor 9 (TLR9) in the response of human neutrophils to H. pylori and purified H. pylori DNA (Hp-DNA). Neutrophils were isolated from the blood of adult volunteers and challenged with either H. pylori or Hp-DNA. We found that both, H. pylori and Hp-DNA induced increased expression and release of IL-8. Furthermore, we showed that TLR9 is involved in the induction of IL-8 production by H. pylori and Hp-DNA. IL-8 production induced by H. pylori but not by Hp-DNA was partially mediated by NF-κB. In conclusion, this study showed for first time that both, H. pylori and Hp-DNA activate TLR9 and induce a different inflammatory response that leads to activation of neutrophils.

MEKK3 and TAK1 synergize to activate IKK complex in Helicobacter pylori infection

Helicobacter pylori colonises the gastric epithelial cells of half of the world's population and represents a risk factor for gastric adenocarcinoma. In gastric epithelial cells H. pylori induces the immediate early response transcription factor nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-κB) and the innate immune response. We show that H. pylori induces in a type IV secretion system-dependent (T4SS) and cytotoxin associated gene A protein (CagA)-independent manner a transient activation of the inhibitor of NF-κB (IκBα) kinase (IKK)-complex. IKKα and IKKβ expression stabilises the regulatory IKK complex subunit NF-κB essential modulator (NEMO). We provide evidence for an intimate mutual control of the IKK complex by mitogen-activated protein kinase kinase kinase 3 (MEKK3) and transforming growth factor β activated kinase 1 (TAK1). TAK1 interacts transiently with the E3 ubiquitin ligase tumor necrosis factor receptor-associated factor 6 (TRAF6). Protein modifications in the TAK1 molecule, e.g. TAK1 autophosphorylation and K63-linked ubiquitinylation, administer NF-κB signalling including transient recruitment of the IKK-complex. Overall, our data uncover H. pylori-induced interactions and protein modifications of the IKK complex, and its upstream regulatory factors involved in NF-κB activation.

A novel NOD1- and CagA-independent pathway of interleukin-8 induction mediated by the Helicobacter pylori type IV secretion system

The type IV secretion system (T4SS) of Helicobacter pylori triggers massive inflammatory responses during gastric infection by mechanisms that are poorly understood. Here we provide evidence for a novel pathway by which the T4SS structural component, CagL, induces secretion of interleukin-8 (IL-8) independently of CagA translocation and peptidoglycan-sensing nucleotide-binding oligomerization domain 1 (NOD1) signalling. Recombinant CagL was sufficient to trigger IL-8 secretion, requiring activation of α5 β1 integrin and the arginine-glycine-aspartate (RGD) motif in CagL. Mutation of the encoded RGD motif to arginine-glycine-alanine (RGA) in the cagL gene of H. pylori abrogated its ability to induce IL-8. Comparison of IL-8 induction between H. pylori ΔvirD4 strains bearing wild-type or mutant cagL indicates that CagL-dependent IL-8 induction can occur independently of CagA translocation. In line with this notion, exogenous CagL complemented H. pylori ΔcagL mutant in activating NF-κB and inducing IL-8 without restoring CagA translocation. The CagA translocation-independent, CagL-dependent IL-8 induction involved host signalling via integrin α5 β1 , Src kinase, the mitogen-activated protein kinase (MAPK) pathway and NF-κB but was independent of NOD1. Our findings reveal a novel pathway whereby CagL, via interaction with host integrins, can trigger pro-inflammatory responses independently of CagA translocation or NOD1 signalling.